''Euchelus atratus'', common name the blackish margarite, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

, a marine

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Chilodontidae.

Description

The size of the shell varies between 5 mm and 21 mm. The solid, umbilicate shell has a globose-conic shape. Its color is black, brown, or grayish-pink, either unicolored or tessellated with dark spots. The conic

spire A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spires are ...

is short. The sutures are deeply canaliculate. The 5-6 convex

whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...

s are encircled by numerous equal, densely, finely beaded spiral ribs, with deep interstices, in each of which an interstitial riblet arises on the last part of the

body whorl The body whorl is part of the morphology of the shell in those gastropod mollusks that possess a coiled shell. The term is also sometimes used in a similar way to describe the shell of a cephalopod mollusk. In gastropods In gastropods, the b ...

. The spiral ribs on the penultimate whorl number 7 to 9. On the body whorl they number 12, exclusive of the interstitial riblets. The convex body whorl is rounded, quite abruptly and decidedly descending at the

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An opt ...

. The rounded aperture is strongly, finely sulcate inside. The

columella Lucius Junius Moderatus Columella (; Arabic: , 4 – ) was a prominent writer on agriculture in the Roman Empire. His ' in twelve volumes has been completely preserved and forms an important source on Roman agriculture, together with the wo ...

is straight, with a small projecting tooth at base. The umbilicus is deep, bounded by a strong white rib, about 1 mm. diameter. Larger specimens (16–23 mm. alt.) are paler, and have a small riblet developed in each interstice, thus about doubling the number of spirals.Tryon (1889), Manual of Conchology XI, Academy of Natural Sciences, Philadelphia
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Distribution

This species occurs in the

Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...

and in the Indian Ocean off the

Mascarene The Mascarene Islands (, ) or Mascarenes or Mascarenhas Archipelago is a group of islands in the Indian Ocean east of Madagascar consisting of the islands belonging to the Republic of Mauritius as well as the French department of Réunion. Their ...

Basin.

References

* Drivas, J. & M. Jay (1988).'' Coquillages de La Réunion et de l'île Maurice'' * Higo, S., Callomon, P. & Goto, Y. (1999) ''Catalogue and Bibliography of the Marine Shell-Bearing Mollusca of Japan''. Elle Scientific Publications, Yao, Japan, 749 pp. * Herbert D.G. (2012) ''A revision of the Chilodontidae (Gastropoda: Vetigastropoda: Seguenzioidea) of southern Africa and the south-western Indian Ocean''. African Invertebrates, 53(2): 381–502

External links

* {{DEFAULTSORT:Euchelus Atratus atratus Gastropods described in 1791